Cochlea

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The cochlea is the auditory portion of the inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating fluid chambers in the coiled tapered tube of the cochlea.

The name is from the Latin for snail, which is from the Greek κοχλίας kokhlias ("snail, screw"), from κόχλος kokhlos ("spiral shell")[1] in reference to its coiled shape; the cochlea is coiled in most mammals, monotremes being the exceptions.

Contents

Anatomy

Structures

The cochlea is a spiralled, hollow, conical chamber of bone. Its structures include:

  • the scala vestibuli (containing perilymph), which lies superior to the cochlear duct and abuts the oval window
  • the scala tympani (containing perilymph), which lies inferior to the scala media and terminates at the round window
  • the scala media (containing endolymph), which is the membranous cochlear duct containing the organ of Corti
  • the helicotrema is the location where the scala tympani and the scala vestibuli merge
  • Reissner's membrane separates the scala vestibuli from the scala media
  • the basilar membrane, a main structural element that separates the scala media from the scala tympani and determines the mechanical wave propagation properties of the cochlear partition
  • the Organ of Corti, the sensory epithelium, a cellular layer on the basilar membrane, powered by the potential difference between the perilymph and the endolymph
  • hair cells, sensory cells in the Organ of Corti, topped with hair-like structures called stereocilia

Function

The cochlea is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear via the oval window. As the fluid moves, thousands of "hair cells" are set in motion, and convert that motion to electrical signals that are communicated via neurotransmitters to many thousands of nerve cells. These primary auditory neurons transform the signals into electrical impulses known as action potential, which travel along the auditory nerve to structures in the brainstem for further processing.

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